(1) Technical Field
The invention relates to a process for preparing a diazocyano acid such as 4,4'-azobis-(4-cyanovaleric acid) using a keto-acid such as levulinic acid or a sodium salt of a keto-acid as the starting material.
(2) Background Information
Diazocyano acids have been used as an initiator for polymerization such as homopolymerization of acrylamide or 1,3-butadiene or copolymerization of 1,3-butadiene with acrylonitrile (see, e.g., Japanese Examined Pat. Publication (Kokoku) No. 43-28474 and Japanese Unexamined Pat. Publication (Kokai) Nos. 56-133305 and 57-198720).
As means for the preparation of diazocyano acids, there is known a process comprising reacting a keto-acid or its sodium salt with a cyanogen compound such as sodium cyanide or hydrogen cyanide and a hydrazine such as hydrazine hydrate in water to form a hydrazo compound, adding chlorine gas to the obtained solution to oxidize the hydrazo compound and form a diazocyano acid and filtering off the solid diazocyano acid from the obtained reaction mixture (see, also, Japanese Examined Pat. Publication (Kokoku) No. 43-28474 and Japanese Unexamined Pat. Publication (Kokai) No. 56-133305).
However, this known process has the following problems:
(a) The yield of the diazocyano acid is low.
(b) Since sodium chloride is formed as a by-product in an amount of at least 2 moles per mole of a diazocyano acid when the diazocyano acid is synthesized, a large amount of sodium chloride is contained in the diazocyano acid product. A diazocyano acid containing a large amount of sodium chloride is not preferred as the initiator for homopolymerization of 1,3-butadiene or copolymerization of 1,3-butadiene with acrylonitrile.
(c) If a refining step is arranged for removing sodium chloride contained in the diazocyano acid, the yield of the diazocyano acid is drastically reduced.